Device for aerating fluids, in particular during flotation

ABSTRACT

Ring injectors for aerating fluids, useful for example in flotation systems, have a housing with a mixing section, in which air is added to the through-flowing fluid through an annular slot. A core is arranged in the center of the mixing section. An air-solid mix is formed in the mixing section by deposition of air bubbles on solid particles. An annular injector with a slot width (Q 2 ) that leads into the airing chamber with a minimum opacifying speed of 2.0 m/s at the inlet of the aerating chamber, has an annex mixing and dispersing section (6) with a cross-section that remains the same until the end (12), as well as a middle piece (10) centrally arranged therein also having a constant cross-section, the length of the mixing and dispersing section (6) being 20 times the width of the annular slot (Q 3 ). The distributing cone (2) and the middle piece (10) can be screwed together or inserted into each other. The air slot can be regulated by spacing rings (13). Screw-shaped strips (8) within the mixing and dispersing section ( 6) can generate therein a whirl. The aerating device has been tested for the flotation of mineral coal sludges.

BACKGROUND OF THE INVENTION

The present invention relates to a device for aerating liquids orfluids, especially during flotation, and is embodied as a ring injector,in the housing of which, through which the fluid flows, there isdisposed a middle piece that forms an annular channel with the housing,whereby at the level of the air discharge openings in the wall of thehousing, the annular channel has its narrowest cross-sectional area;following this narrowest location of the annular channel in thedirection of flow of the fluid, the annular channel undergoes a suddenincrease in cross-sectional area, adjoining which a mixing anddispersing section leads to the outlet of the housing.

Devices of this type are known, and are used, for example, duringflotation in order to separate the solid materials contained in a slurryfrom one another. The difficult-to-moisten solid particles are depositedon air bubbles that are generated in such devices, which are also knownas gasifiers, injectors, or reactors. The solid material deposited onthe air bubbles is generally discharged over the edge of the separatingor flotation vessel.

With all aerating devices of this type it is desirable to keep the sizeof the air bubbles as small as possible, because this facilitates thedeposition of solid particles during the flotation.

A device for mixing gases and liquids was already disclosed 50 years agoin U.S. Pat. No. 1,810,131. This device shows features of an aeratingdevice such as was later disclosed (DE-OS No. 34 12 431) as a device foraerating dispersions, especially as a flotation device for deliveringfibrous material suspensions or dispersions with a ring injector.

Air is supplied to the ring injector via air supply passages in themixing section. As a result, the annular gap formed in the ring injectoris aerated on the inside and the outside. The mixing section and themiddle piece, which is centrally disposed within the mixing anddispersing section, are stepped, as a result of which, similar to awater-jet pump, the air is drawn into the inner and outer regions of thedispersion stream that is formed.

It is an object of the present invention to substantially improvedevices of the aforementioned general type so that the specific energyconsumption is reduced and the degree of selectively is increased.

This device should be especially suitable for the flotation of coal andother preparation material.

SUMMARY OF THE INVENTION

To realize this object, it is proposed pursuant to the present inventionthat the aerating device of the aforementioned general type have, as theslurry enters the aeration chamber, a gap width that leads to a minimumslurry speed V₁ of 2.0 m/s. The middle piece of the device extends tothe outlet of the housing and the diameter remains constant. The annularchannel has the same cross-sectional area from the sudden increase tothe outlet of the housing, and the length of the mixing and dispersionsection is more than 20 times the annular gap width of the annularchannel.

Due to the uniform speed in the annular channel resulting from theconstant cross-sectional area, the thorough mixing of air bubbles andsolid material particles during the course of the mixing section isparticularly favorable, since during the course of the entire mixingsection the specific energy input is constant.

Tests in a coal-flotation plant have shown that at a slurry speed ofgreater than 2 m/s, especially at 2.0 to 4.0 m/s, the yield is optimum.

Further structural details will be described in detail subsequently.

The splitting of the core or essential portion of the aerating deviceinto the distributing cone and the middle piece, which can be screwedtogether or inserted into one another, makes it possible to combinedifferent distributing cones and middle pieces. Depending upon therequirements, it is possible to use distributing cones having differentdiameters of the base of the straight circular cone, and/or cones havingdifferent angles between the base and the side lines of the circularcone, i.e. with increased or decreased slope. By changing the basediameter of the distributing cone, the cross-sectional area of theannular channel is varied at the level of the air discharge openings.The slurry distribution can be influenced by the angle of inclination ofthe cone.

The strips disposed on the middle piece and/or in the upper part of thehousing serve to center the middle piece within the mixing anddispersion section. Such strips can also have a helical shape, and ithas been shown that in so doing a swirl flow overlaps the axial flow ofthe slurry-air-mixture; this swirl flow has an advantageous effect uponthe deposition of the solid particles on the air bubbles.

This is also true for the embodiment of a helically grooved or slottedmiddle piece and/or a similarly grooved or slotted inner wall of theupper part of the housing. In this case, centering of the middle piececan be effected, for example, by centering pins that hold the middlepiece in the upper part of the housing.

                                      TABLE 1                                     __________________________________________________________________________    Test conditions and results with different                                    ring injectors                                                                                             Mater-                                                   Length      Retention                                                                              ial  Ash                                                 L.sub.1 of  time in  yield                                                                              content                                     Gap     the     Slurry                                                                            the  Deliv-                                                                            in the                                                                             in the                                      width   mixing  speed                                                                             mixing                                                                             ery ash                                                                           concen-                                                                            concen-                                     Q.sub.2 section                                                                           Ratio                                                                             v.sub.1                                                                           section 6                                                                          content                                                                           trate                                                                              trate                                       (mm)    (mm)                                                                              L.sub.1 /Q.sub.2                                                                  (m/s)                                                                             (s)  (a %)                                                                             (m %)                                                                              (a %)                                       __________________________________________________________________________    Type 1                                                                            6   125 20.8                                                                              9.1 7.3 · 10.sup.-2                                                           21.4                                                                              55.5 7.4                                         Type 2                                                                            3   125 41.7                                                                              24.5                                                                              5.1 · 10.sup.-3                                                           22.5                                                                              64.6 7.5                                         Type 3                                                                            5   600 120.0                                                                             14.8                                                                              4.1 · 10.sup.-2                                                           20.4                                                                              70.9 4.9                                         __________________________________________________________________________

Table 1 shows the test conditions and test results that were achievedwith inventive ring injectors of the Types 1 to 3. During the flotationtests, at half of a commercial scale, a flotation slurry from a mineralcoal wash was used as the feed material.

BRIEF DESCRIPTION OF THE DRAWING

One exemplary embodiment of the inventive aerating device is describedin detail with the aid of the schematic drawing.

DESCRIPTION OF PREFERRED EMBODIMENTS

The cross-sectional view of the illustrated aerating device comprises amulti-part housing. The lower part (3) of the housing is provided withthe connection flange (1) to which the (not illustrated) slurry line isconnected. The arrow indicates the direction of flow of the slurry. Theinlet diameter of the aerating device is designated by (Q₁).

Connected to the lower part (3) of the housing is a housing section inwhich is disposed the air chamber (4) with the annular air dischargeopening. The aerating medium flows to the air chamber (4) via a (notillustrated) air line.

By inserting spacer rings (13), the gap width of the air dischargeopenings in the annular gap of the air chamber (4) can be varied.

Disposed above the lower part (3) of the housing with the air chamber(4) is the upper part (7) of the housing. The flange (5) serves for thesecurement of the aerating device within a line to the (not illustrated)separating vessel or, where the aerating device is disposed externallyof the separating vessel, as a line connection on the separating vessel.

Disposed within the housing of the aerating device is the core oressential portion, which comprises a distributing cone (2) and themiddle piece (10). The distributing cone and middle piece can be screwedtogether or inserted into each other. The separating location is at thetransition of the reduction of the cross-sectional area of thedistributing cone to the middle piece of uniform diameter. The middlepiece (10) has a diameter that is uniform over its entire length to theoutlet (12) of the housing.

Disposed at the level of the air outlet from the air chamber (4) is thenarrowest location of the annular channel for the through flow of theslurry. This narrowest location (Q₂) is formed by the largest diameterof the distributing cone (2). The abrupt increase (11) in thecross-sectional area of the annular channel between the distributingcone and the inner wall of the upper part of the housing, which increasein the cross-sectional area results from the structural configuration ofthe upper portion of the distributing cone (2), prevents, despite thefact that air is received from the air chamber, an increase in the speedin the flotation slurry.

Adjoining the narrowest location of the annular channel is the mixingand dispersing section (6), which has a length L₁ and a uniform gapwidth (Q₃) until the outlet (12) of the housing.

Indicated on the middle piece (10) is a helically disposed strip (8)that is intended for centering the middle piece in the upper part (7) ofthe housing and for generating a swirl flow of the slurry-air-mixture.

A holding mechanism (9) in the form of an adjustable pin is disposed onthe upper part (7) of the housing below the outlet (12) of the housing.

The present invention is, of course, in no way restricted to thespecific disclosure of the specification, Table 1, and drawing, but alsoencompasses any modifications within the scope of the appended claims.

What we claim is:
 1. A device for aerating fluids and embodied as a ringinjector comprising:a housing through which said fluid, in the form of aslurry, flows, with said housing having an inlet end, an outlet end, andair discharge opening means; and a middle piece disposed in said housingin such a way that an annular channel is formed between said middlepiece and said housing, with said middle piece having an end that isremote from said outlet end of said housing and that is embodied in sucha way that at this location, where said annular channel communicateswith said air discharge opening means of said housing, said annularchannel increased suddenly, in the direction of flow of said slurry,from its narrowest gap width, which leads to a minimum slurry speed of2.0 m/s, to a uniform cross-sectional area having a wide gap width thatremains constant to said outlet end of said housing and that provides amixing and dispersing section, the length of which is more than twentytimes said constant wider gap width.
 2. A device according to claim 1,in which said remote end of said middle piece, where said annularchannel increases suddenly, is formed by a separate piece in the form ofa distributing cone, with said middle piece and distributing cone beingconnected to one another and forming the core of said aerating device.3. A device according to claim 2, in which said middle piece and saiddistributing cone are connected by being screwed together.
 4. A deviceaccording to claim 2, in which said middle piece and said distributingcone are connected by being inserted into one another.
 5. A deviceaccording to claim 2, which includes means for varying the size of saidair discharge opening means of said housing.
 6. A device according toclaim 5, in which said housing includes a lower part that is providedwith said inlet end, an upper part that is provided with said outletend, and between said lower and upper parts a section that is providedwith said air discharge opening means and an air chamber that isconnected to a supply of air and communicates with said air dischargeopening means.
 7. A device according to claim 6, in which said means forvarying the size of said air discharge opening means is in the form ofspacer rings that are adapted to be disposed between said lower part ofsaid housing and said housing section that is provided with said airchamber.
 8. A device according to claim 6, which includes at least onestrip means that is uniformly disposed in said mixing and dispersingsection and extends from where said annular channel increases suddenlyto said outlet end of said upper part of said housing.
 9. A deviceaccording to claim 8, in which said strip means is uniformly disposed onthe periphery of said middle piece.
 10. A device according to claim 8,in which said strip means is uniformly disposed on an inner periphery ofsaid upper part of said housing.
 11. A device according to claim 8, inwhich said strip means is uniformly disposed on both the periphery ofsaid middle piece and an inner periphery of said upper part of saidhousing.
 12. A device according to claim 8, in which said strip meanshas a helical configuration with at least one screw thread.
 13. A deviceaccording to claim 6, in which at least one of said middle piece and aninner wall of said upper part of said housing is provided with helicalgroove means.